Many methods have been known as electrophotography. In general, such methods each comprises the process of forming an electrostatic latent image on a photosensitive member by various means using a photoconductive material (exposure process), the development process of developing the latent image by the use of a toner, the transfer process of transferring a toner image to a transfer material such as paper, and the fixing process of fixing the toner image by heating and pressurization using a fixing roll.
In order to effectively transfer the toner image in the transfer process, it has been conducted that a wax excellent in releasability is added to the toner.
The wax-containing toner is usually produced as described below.
First, a raw material containing a resin that is a main component (hereinafter also briefly referred to as a “resin”), a coloring agent and the wax is kneaded at a temperature equal to or higher than the softening point of the resin to obtain a kneaded material. The kneaded material thus obtained is cooled to a temperature equal to or lower than the melting point of the resin, and then pulverized. An additive (external additive) is further added as needed to produce the intended toner.
Now, in general, wax is known to be low in compatibility with a resin, a main component of a toner. Accordingly, in order to sufficiently finely dispersing the wax, kneading treatment for thoroughly kneading the above-mentioned raw material has been conducted.
However, in a case where the content of the wax is relatively increased in order to obtain sufficient releasability, wax particles cannot be sufficiently finely dispersed in toner particles finally obtained, in some cases, even when the kneading treatment is sufficiently conducted. When the wax particles cannot be sufficiently finely dispersed like this (when the wax particles are coarsened), the wax oozes out remarkably. The wax that has oozed out adheres to the photosensitive member in large amounts (filming) in some cases. When the wax adheres to the photosensitive member like this, it has sometimes happened that the transfer efficiency of the toner to the transfer material rather decreases. The toner in which the wax particles are coarsened decreases in its mechanical strength to cause poor durability. Further, the toner in which the wax particles are coarsened also has the problem that a so-called fogging phenomenon is liable to occur.
On the other hand, when the content of the wax is decreased in order to prevent the wax particles from being coarsened as described above, sufficient releasability is not obtained, resulting in a decrease in the transfer efficiency to the transfer material.